The objectives of this study are the following: 1) To determine the efficacy of hepatitis B immune globulin (HBIG) in altering the incidence of hepatitis B infection in infants born to (1) chronic HBsAg carrier mothers and to (2) mothers with acute hepatitis B during the third trimester of pregnancy and immediate two month post-partum period. 2) To investigate the value of viral markers of the type B hepatitis virus in determining the frequency of maternal-infant transmission in HBsAg positive carrier mothers and the effect of HBIG on the appearance of these viral markers in the infants. 3) To study the natural course of hepatitis B infection in children found to be HBsAg positive during the course of this research project. 4) To determine the incidence of HBsAg infection in family members of HBsAg carrier mothers and HBsAg positive infants. 5) To study acute A and acute non-A non-B hepatitis infection in pregnant females and its possible transmission of infection to their newborn infants.